Banca de DEFESA: MATEUS SILVA RÊGO

Uma banca de DEFESA de DOUTORADO foi cadastrada pelo programa.
DISCENTE: MATEUS SILVA RÊGO
DATA: 09/03/2026
HORA: 15:00
LOCAL: Remota (On-line)
TÍTULO: Propriedades físicas de nanoestruturas grafínicas 1D e 2D baseadas na rede bifenilênica: um estudo via Teoria do Funcional da Densidade
PALAVRAS-CHAVES: Grafinos; Bifenileno; Estrutura de bandas eletrônicas; Modulação de gap, Ligações acetilênicas.
PÁGINAS: 217
GRANDE ÁREA: Ciências Exatas e da Terra
ÁREA: Física
RESUMO:

The search for new two-dimensional carbon allotropes has
intensified due to the potential of these materials in nanoelectronics,
especially as alternatives to graphene, whose absence of a band gap limits its
applications in semiconductors. Graphyne-like structures, characterized by
the coexistence of and sp sp2 hybridizations, allow the modulation of
electronic properties through structural variations. With the synthesis of the
biphenylene monolayer (BPN), it becomes possible to theoretically investigate
new structures derived from its crystalline network with incorporated
acetylenic linkages. The objective of this thesis is to theoretically investigate,
through the formalism of Density Functional Theory (DFT), the structural,
electronic, and mechanical properties of a new two-dimensional carbon
allotrope derived from BPN, which we denote as ɑ-BPNGY or BPN graphyne,
as well as its quasi-one-dimensional systems, such as nanoribbons and
nanotubes. In this context, we propose to evaluate the structural and
mechanical stability, anisotropy, band structure, density of states (DOS), and
the spatial distribution of the wave functions, as well as the influence of
width, diameter, and chirality in the quasi-1D systems. The results indicate
that the proposed two-dimensional structure is metallic in the non-spin-
polarized (NP) state, but becomes semiconducting in the antiferromagnetic
(AFM) state when the bipartition of the lattice into spin sublattices is
considered, with the opening of a gap on the order of 0.15 eV. The mechanical
stability of ɑ-BPNGY was confirmed by the absence of negative frequencies in
the phonon dispersion, and its thermal stability was evidenced by ab initio
Born–Oppenheimer molecular dynamics (BO-MD) simulations. It was
observed that increasing the number of acetylenic units ( = 1, 2, and 3; n
where indicates the number of acetylenic links) directly influences the n
mechanical properties, imparting anisotropy to the investigated systems (ɑ-
BPNGY, ɑ-BPNGY-2, and ɑ-BPNGY-3). In the quasi-1D systems, the electronic
behavior of nanotubes depends on chirality and diameter, whereas that of
nanoribbons depends on width. The evaluated nanoribbons are
semiconducting, with gaps ranging from 0.07 to 0.46 eV. Most of these one-
dimensional systems exhibit a spin-polarized semiconducting state similar to
that observed in the two-dimensional system. These findings highlight the
possibility of fine-tuning the electronic properties, emphasizing the potential
of these materials for nanoelectronic applications.

MEMBROS DA BANCA:
Externo à Instituição - 600.***.***-75 - DIEGO RABELO DA COSTA - UFC
Interno - 1548848 - EDUARDO COSTA GIRAO
Externo à Instituição - 655.***.***-53 - JOÃO ALBERTO SANTOS PORTO - UEMA
Presidente - 1250015 - PALOMA VIEIRA DA SILVA
Externo à Instituição - 380.***.***-00 - SÉRGIO ANDRE FONTES AZEVEDO - UFPB
Externo à Instituição - 665.744.37-1 - VINCENT MEUNIER - Penn State (